there are a few methods out there creating an upper arm roll, however, none of those methods work in all possible situations, so it's quite normal you will have to switch to one of 2 solutions (like backwards and forward arm or something like this). if you actually animating and come to this area you have a problem...
so for my diploma thesis i came up with the following method i like to share with you.
- You will need an upper arm with at least 2 joints, better 3 or 4 to
give a nice volume preservation. Then you will need also a driver arm
setup for the ik with just 2 bones. The chains must have the same
LRA-Orientation for this setup to work.
- Create a rotate-plane ik fort he ik-joints. This will be a simple arm-setup to later drive the deform joints.
- Now comes the funky part
Create another rotate-plane ik for the first deform joint, set the polevector of the rotate-plane ik to 0-0-0. By doing this the ik will remember its orientation and will ony flip if the ik-handle gets to the exact opposite. This trick will ensure the the first deform joint will not self-rotate, it will always keep its original orientation. This ik-setup acts a little bit like a aim-constraint.
- Now parent the rp-ik to the first upper-arm joint from the driver
ik-chain. By doing the deform-chain will follow the driver-chain
without doing the self-rotation. And thats exactly what we wanted: NO
SELF ROTATION !!!
- The next step is, you guessed it, to apply the exact self-rotation
or roll-difference gradually back to next 3 joints of the deform chain.
To measure this difference we create a locator, which we parent under
the non-self-rotating first deform-joint. Then we create an orient
constraint from the first driver-ik-joint to the locator. This way the
locator rotates with driver-chain, but since its parented to the
deform-chain, which also rotates with the driver, except for the
roll-component, you get the exact rotation difference.
- The last step is take the rotate value of the locator and divide
it through the number of deform-joint 1 and connect this value to the
- The Setup is finished. You will see it produces very stable
results. It will never flip unless the arm is positioned to the
opposite, which is for more or less every character impossible.
Hope you liked the Tutorial!
also visit my homepage: https://www.ferstltom.com/
Submitted: 2009-05-04 16:48:55 UTC
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